Hydrogen-Peroxide Metabolism in Skeletal-Muscle Mitochondria

The presence of catalase in heart mitochondria may prevent excessive H2O2 from reaching the cytosol, eventually reacting with myoglobin (R. Radi et al., 1991, J. Biol. Chem. 266, 22028-22034). In this report we investigated whether catalase was also present in the mitochondrial matrix of skeletal muscle as it also contains myoglobin which could react with H2O2 produced by mitochondria. Catalase content of skeletal muscle tissue was about 1.4% of that in liver. Simultaneous determinations of citrate synthase (a mitochondrial marker) and catalase in intact mitochondria and mitoplasts indicated that catalase is not associated with muscle mitochondria. The lack of catalase in muscle mitochondria is not due to a limited H2O2 production by these organelles. Rat skeletal muscle mitochondria generated H2O2 (0.64 ± 0.04 nmol/(min · mg protein), approximately 40% the rate in heart mitochondria. Other groups have shown that training causes an increase in the concentration of mitochondrial electron carriers as well as an increase in the activity of mitochondrial glutathione peroxidase and mitochondrial electron carriers. The increased concentration of mitochondrial electron carriers and the sudden changes in oxygen supply may lead to increased intracellular H2O2 during exercise.